The invention relates to a disk brake rotor with a wear indicator that does not affect operation of the rotor yet allows easy visual inspection of brake rotor wear without having to remove the brake rotor from the vehicle. The wear indicators of the invention provide both an indication of how much wear is occurring to the rotor as well as a relative estimation of how much acceptable service life remains prior to requiring replacement.
Conventional disk brake rotors generally include a pair of mutually spaced-apart annular disks that form two opposed planar brake contact surfaces. These opposed brake contact surfaces receive braking force as applied by a brake caliper through two opposed brake pads. The rotors encounter frictional forces and heat buildup whenever the brakes are applied. While the brake pads are designed to wear and be replaced, the rotor can also wear or become damaged due to heat degradation and material fatigue caused by the cyclical application of frictional brake forces. Eventually, the brake pads can become worn to a point where replacement is necessary. The full life expectancy of brake pads and rotors cannot be precisely determined in advance as this would depend upon a number of variables such that it will be different for each vehicle and driver. For this reason, periodic inspection of brake pads and rotors is necessary.
Brake pads are designed to include visual or audible indications of brake pad life. These can include metal wear indicators located to one side of the brake pad, which generally exhibit an audible sound when the brake pads are sufficiently worn to a point where the metal indicators contact the rotor surface during braking. More complex indicators on some vehicles activate circuits that illuminate a warning indicator when brake pads are worn down too far. In contrast, the wear on brake rotors is not as readily ascertainable. Each brake rotor is designed for a particular application and has a minimum dimensional thickness after which time the brake rotor no longer operates in as safe capacity and requires replacement. Generally, vehicle manufacturers prefer smaller margin of wear on brake rotors to control vehicle weight and gas mileage. It is therefore imperative that these rotors be inspected to assure that they have sufficient thickness to facilitate an acceptable braking performance.
While a severely uneven, pitted or scored contact surface on a brake rotor may be quickly identified by a trained mechanic's eye, the remaining life of a rotor that does not contain such serious defects cannot be readily determined visually. It cannot be assumed that the wear will be uniform during further vehicle operation, and because different rotors have differing dimensions and design criteria, a visual inspection is not considered. Instead, conventional inspection techniques involve precise measurements of the rotor contact surfaces using micrometers or similar equipment. Such rotor inspections require expensive and properly calibrated equipment as well as the knowledge of the appropriate minimum thickness for the rotor. This adds cost and complexity to a proper determination of rotor condition.
One prior solution to this problem is an implementation by the original automotive manufacturer as well as by aftermarket manufacturers to engrave a logo of minimum thickness somewhere on an outward facing surface of the rotor. The disadvantage of this procedure is that the rotors are primarily made of iron which rusts thus obscuring the minimum thickness engraving so that it is very difficult or not possible to accurately gauge remaining useful life in the rotors. This is procedure is also very time consuming.
There have been other attempts in the prior art to provide visual wear indicators on brake rotors. For example, U.S. Pat. No. 6,457,566 discloses a brake rotor that includes at least one visual wear indicator formed on either the inboard or outboard break contact the surface. These indicators include a recess surface that is substantially parallel to the break contact surfaces and that has a depth corresponding to a minimum usable thickness of the rotor. This patent discloses a single wear indicator near the outer portion of the brake pad contact surface in order to indicate wear in that area. While this is useful, it only provides an indication of when the rotor may still provide acceptable performance and only when the wear indicator is no longer visible, is there an indication that the brake rotor must be replaced. As such, the patent does not disclose or suggest how much time it might take before replacement is needed.
U.S. Pat. No. 6,279,698 also discloses a brake disc that has wear visual control components in the form of radial grooves shaped as a circle and applied upon the swept braking surface of the disk. These grooves are intended to remove water from the surface of the brake disc but by controlling the depth of the grooves, they can also act as wear visual control means. Again, however, these merely indicate that when the grooves disappear or are just visible, the brake disc has reached its maximum wear limit and must be replaced. The patent does disclose that one of the radial grooves may have a depth of about 0.1 to 0.3 mm shallower than the others, so as to act as an indication of the imminent complete wear of the disc, but this only signifies that the rotor is nearing the end of its useful life without providing any indication of how much time, quantitatively or relatively, might occur before rotor replacement is needed.
Accordingly, there is a need for a brake rotor that is capable of a simple visual inspection to determine remaining useful life or wear conditions that suggest replacement, and these are now provided by the present invention.